1. Field
Provided is a white light emitting diode (“LED”) and a liquid crystal display device including the same.
2. Description of the Related Art
A white light emitting diode using a semiconductor is in the spotlight as one of next generation light emitting devices that are capable of replacing existing light emitting devices, due to its long life-span, capability of being down-sized, low power consumption, and environmentally friendly characteristic of being mercury free. The white light emitting diode is also used for an instrument panel of automobiles, a backlight of liquid crystal displays (“LCDs”), and the like.
Particularly, for use as a backlight of a liquid crystal display, a method of using a tri-color (red, green, and blue, or “RGB”) light emitting diode having excellent efficiency and color purity has been suggested, however it has a drawback of poor price competitiveness due to its high manufacturing cost and complicated operation circuit. Thus, there is a demand for the development of a one chip solution that can reduce manufacturing cost and simplify the construction of a device, while maintaining efficiency and color purity performance similar to the existing method.
As one of the one chip solutions, a white LED that combines an indium gallium nitride (InGaN) series blue light emitting diode having a wavelength of about 450 nanometers (nm) with a cerium-doped yttrium aluminum garnet (YAG:Ce) phosphor has been developed. The operation principle of the light emitting diode is that a part of blue light generated in the blue light emitting diode excites the YAG:Ce phosphor to generate a yellow-green color, and the blue and yellow-green colors are combined to emit white light.
However, since the white LED light combining the blue light emitting diode with the YAG:Ce phosphor has only a part of the spectrum of the visible ray region, it has a low color rendering index, and when passing through a red, green, or blue color filter, many light components fail to pass through the color filter thus causing efficiency loss. Thereby, it has low color purity and thus is not suitable for a display device requiring high definition such as a television (“TV”).
A method of manufacturing a white light emitting diode using an ultraviolet (“UV”) light emitting diode that is expected to have high energy efficiency as an excitation source rather than a blue light emitting diode, and using a blue, green, and red light emitting source, has been researched. However, it is required to develop a red light emitting source having high efficiency compared to blue and green.
As another method, a method of coating green and red inorganic phosphors on a blue light emitting diode has been attempted. However, a suitable material that is capable of exciting an inorganic phosphor that is excited by relatively high energy to a blue wavelength of the visible light region has not yet been developed, and a thus-far developed green phosphor has low stability and color purity. Further, a problem of low efficiency of a red phosphor has not yet been settled, and thus the method has a limitation in that color purity and light efficiency required in a light emitting diode for a backlight unit cannot be secured.